Field of the Invention
The present invention relates to a cooling control system for an internal combustion engine that includes a supercharger, the cooling control system being provided for cooling intake gases which have been increased in temperature by being pressurized by the supercharger.
Description of the Related Art
In general, in an internal combustion engine equipped with a supercharger, a cooling control system including an intercooler cools intake air which has been increased in temperature by being pressurized by a supercharger, in order to avoid occurrence of knocking or the like while ensuring improvement of power output. Conventionally, as a cooling control system of this kind, there has been known one disclosed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 2014-156804. This cooling control system includes an intercooler of the water cooled type, a radiator, an engine coolant passage for connection therebetween, and an electric pump that delivers engine coolant to circulate the same. The intercooler is disposed in an intake passage of the engine at a location downstream of a compressor of the supercharger, and engine coolant is circulated between the intercooler and the radiator by operation of the electric pump. With this, intake air pressurized by the supercharger and passing through the intercooler in the intake passage is cooled by heat exchange with the engine coolant to become lower in temperature.
Further, the above-mentioned engine is equipped with an EGR device for recirculating part of exhaust gases discharged into an exhaust passage (hereinafter referred to as the “EGR gases”) to an upstream side of the intercooler in the intake passage. Therefore, when EGR (exhaust gas recirculation) is being performed, the intake air and the EGR gases (hereinafter, collectively referred to as the “intake gases”) are cooled via the intercooler, and are introduced into cylinders of the engine in a state lowered in temperature.
The EGR gases usually includes a relatively large amount of water vapor, and hence if the intake gases are excessively cooled by the intercooler, the water vapor in the intake gases is condensed when the intake gases pass though the intercooler, whereby condensed water is sometimes generated in the intake passage. When such condensed water is attached to a component part of an intake system including the intercooler, the component part can be corroded. To avoid this inconvenience, in the above-described cooling control system, the temperature of the intake gases at an outlet of the intercooler (hereinafter referred to as the “outlet temperature”), that is, the temperature of the intake gases cooled by the intercooler is compared with the dew-point temperature at that time are compared, and the outlet temperature is controlled such that it becomes higher than the dew-point temperature.
More specifically, when the outlet temperature is higher than the dew-point temperature, the electric pump is operated to circulate engine coolant, whereby the temperature of the intake gases is lowered. On the other hand, when the outlet temperature is not higher than the dew-point temperature, the electric pump is stopped and in addition, engine coolant for cooling an engine body, which is relatively high in temperature, is caused to flow into the intercooler, whereby the temperature in the intercooler is raised. Through this operation, the outlet temperature is made higher than the dew-point temperature, to thereby prevent condensed water from being generated when intake gases is cooled by the intercooler.
As described hereinabove, in the above cooling control system, the outlet temperature is adjusted by controlling the operation of the electric pump according to the above-described outlet temperature and dew-point temperature. However, since the outlet temperature is adjusted with reference to the dew-point temperature, there is a fear that the electric pump is operated more than necessary although the outlet temperature is lowered close to the dew-point temperature, whereby a large amount of electric power is consumed to exert an adverse influence on fuel economy. Further, when intake gases having a relatively high temperature is introduced into the intake passage in a stopped state of the electric pump, the intake gases cannot be properly cooled, which sometimes causes reduction of the power output of the engine.